The long-term goals of this project are to continue to develop methods for studying the development of visual function in human infants, and to carry out substantive studies of the development of visual functions, including visual acuity and color vision. The goal for the next five years is to concentrate on the use of transient pupillary responses as the measurement technique for these studies. In addition to its sustained changes in diameter with changes in light levels, the pupil of the eye exhibits transient constrictions to many different kinds of changes in the visual environment. For example, the pupil will constrict if a green spot is replaced for a red one, and constrict again if the red spot is replaced by the green one, even if the red and green are matched in brightness; and it will constrict if the black and white stripes of a black/white grating are exchanged in position. Both of these examples involve changes in the stimulus pattern without changes in the mean light level entering the eye. Infants' pupils are responsive to illumination changes from birth onwards, and they exhibit transient pupillary responses to at least some isoluminant exchanges. It seems likely that the development of transient pupillary responses to chromatic exchanges and to black/white reversals can be used to study aspects of the development of color vision and visual acuity respectively. The specific aims of this proposal are: 1) To refine and optimize methods for studying the transient pupillary response in infants of various ages. 2) To carry out substantive studies of the development of visual acuity and color vision in infants.